This invention relates to the manufacture of parts using sheet metal forming blanks and forming dies and more particularly to new and improved superplastic forming die constructions and techniques for the simultaneous superplastic forming of metallic blanks into a plurality of formed parts.
Prior to the present invention, various types of superplastic forming equipment and processes have been developed for forming blanks of metallic materials into a wide range of items. The forming dies for such equipment and processes are operated in presses that are capable of maintaining elevated temperatures necessary for superplastic forming. Such temperature elevation increases the capability of the metal for strain induced deformation and reduces the force required for that deformation. A time controlled compressed air charge is typically delivered to the forming equipment to apply the force on the heated metal blank to super plastically form the metal on the forming die.
In more specific detail relative to the present invention, superplastic forming involves the employment of a blank ductile sheet of superplastic metal alloy heated by heat energy sustained in a heated press and stretched by the applied force of compressed air onto the forming surfaces or into forming cavities of heated forming dies to produce high-quality, light-weight parts such as panels for automotive vehicles. Often such sheets are quite large so that trunk lids, engine hoods or other large panels can be readily formed in one piece.
Examples of such processes and equipment are found in U.S. Pat. No. 5,974,847 issued Nov. 2, 1999 to Sanders et al for Superplastic Forming Process; U.S. Pat. No. 5,819,572 issued Oct. 13, 1998 to P. E Krajewski for Lubricating System For Hot Forming and U.S. Pat. No. 6,047,583 issued Apr. 11, 2000 to G. L. Schroth for Seal Bead For Superplastic Forming of Aluminum Sheet, all assigned to the assignee of this invention and hereby incorporated by reference.
In the patent to Sanders et al. a blank of sheet of metal alloy is heated to a superplastic forming temperature and is pulled over and around a forming insert in a die set. Subsequently using differential gas pressure, the blank is further stretched into conformity with a forming surface of the insert so that thinning of the formed part is minimized. In the patent to Krajewski, dry lubricant is applied to a sheet metal blank which is subsequently heated to predetermined forming temperatures and formed into a part in superplastic forming die equipment. The lubricant initially provides improved forming of the part and subsequently improved release of the formed part from the forming die. In the patent to Schroth a new and improved seal bead construction is provided for superplastic forming tools to improve gas sealing in the tools for augmenting subsequent superplastic stretch forming of the sheet metal blank.
While the above identified patent disclosures provide improvements in superplastic forming they often do not attain new and higher production output and quality standards required for mass production of such formed parts.
In contrast the prior art, the present invention increases superplastic forming production rates by providing for the simultaneous formation of at least two sheets of superplastic forming blanks into two separate parts from the same pressurization. In one preferred embodiment, a lower superplastic formable blank is placed onto a lower die half of a pair of heated superplastic forming die. An upper superplastic formable blank is placed directly on top of the lower blank or panel. A heated upper die half is moved under load onto the upper blank to effect partial fluid sealing at predetermined peripheral interface areas to define a partially sealed air space between the blanks. A pressurization wedge is moved from one side of the overlying sheets to a fluid sealing or stopper position between the sheets and in which a forward edge portion of the upper sheets is displaced upwardly to define a gas entry way between the two blanks and to complete the pressure sealing of the air space between the blanks. Pressurized air or other inert gas is fed through at least one fluid conducting passage formed through the wedge and within the bounds of the pressure sealing of the two heated sheets that effects the simulations displacement of the sheets from one another onto the forming dies to form the two discrete parts.
More particularly, the lower forming blank is sized and initially placed in such a manner that it rests on the lower die half below the leading edge of the pressurization wedge of the equipment of this invention. The upper forming blank is longer than the lower forming blank and when positioned directly on top of the lower forming blank, drapes onto or over the pressurization wedge. The upper and lower forming blank may be loaded on the forming die as a pair of panels or blanks. The clamping of the blanks between the die halves such as by closing operation of a press effects partial internal and perimeter fluid sealing of the blanks and subsequent movement of the pressurization wedge into an air tight or stopper position between the two blanks completes the perimeter sealing required for the following pressurization of the panels for the forming step of the cycle. Pressurized air or other inert gas is fed through at least one fluid flow feed passage extending through the pressurization wedge terminating at points interior of the continuous air seal provided between the overlying sheets and the pressurization wedge forced between the two sheets. The heated blanks are then displaced by the force of the expanding gas introduced between the blanks in opposite directions around or into the forming surfaces of the opposing and closed upper and lower dies. Two high quality superplasticly formed parts are produced from a single air charge. The opened dies can then be quickly prepared to make subsequent pairs of parts in additional cycles.
The equipment of this invention provides improved superplastically formed parts and improved production rates of superplastically formed parts. This invention importantly meets higher standards for quantity production of high quality parts superplastically formed from metallic sheets or blanks operatively mounted in hot forming dies particularly using a press and operating at elevated temperatures.
It is a feature, object and advantage of this invention to provide new and improved equipment and methods to produce superplastically formed parts in which a common pressurized gas is introduced between heated blanks, fluid sealed with respect to one another for superplastic forming to displace the blanks away from one another within forming dies to simultaneously form discrete parts reproducing the form set by the upper and lower profiled forming surfaces.
In one preferred form of the invention, the equipment comprises upper and lower forming dies for superplastically forming sheet metal blanks operatively mounted therebetween and further comprises a blank positioning and air sealing wedge positioned so that it operatively fits between portions of the blanks for the fluid sealing thereof. The wedge importantly establishes the position of an air discharge port for the delivery of a pressurized forming gas therebetween to plastically force the blanks in opposite directions around the profiling surfaces of the forming dies.